I'm not entirely sure if you're using Vault or not - if migrating to a new server involved a new Vault Installation, and you're using Vault Content Center, then you're asking about migrating a Vault library.
If you're using local content center, then the *default* path is usually C:\ProgramData\Autodesk\Inventor 2018\Content Center\Libraries, and you're looking for the custom *.idcl files. I'm not sure if your installation might have this pointed somewhere on a network drive, so that path might vary.
You can double check where IV is looking by going into Projects>Configure Content Center Libraries (icon bottom right) and checking the library path at the top.
Todd
Product Design Collection (Inventor Pro, 3DSMax, HSMWorks)
Fusion 360 / Fusion Team